Remove wrong docstring entries

Author: uvchik

windpowerlib/wind_farm.py

@@ -210,11 +210,6 @@ def nominal_power(self):
 
         See :attr:`~.wind_farm.WindFarm.nominal_power` for further information.
 
-        Parameters
-        -----------
-        nominal_power : float
-            Nominal power of the wind farm in W.
-
         Returns
         -------
         float
@@ -313,10 +308,6 @@ def assign_power_curve(self, wake_losses_model='wind_farm_efficiency',
             Turbulence intensity at hub height of the wind farm for power curve
             smoothing with 'turbulence_intensity' method. Can be calculated
             from `roughness_length` instead. Default: None.
-        roughness_length : float (optional)
-            Roughness length. If `standard_deviation_method` is
-            'turbulence_intensity' and `turbulence_intensity` is not given
-            the turbulence intensity is calculated via the roughness length.
 
         Returns
         -------